Holley stumble trouble
It happens at very light throttle while cruising when I try to roll into it
Most likely cause is
Transfer slots are .045” exposed
Holley's Mike Urich gave the typical working range as .020 to .040"
Secondaries of course usually not exposed at all.
You mean the mix screws. Yes?
That's a good start. But the important thing is that the idle changes when you adjust them.
Reduce the throttle position, and readjust the mixture for strongest rpm in gear. Or go leaner until the rpm just begins to drop, then turn 1/4 back richer.
Should I start by drilling out the IFRs?
NO
Where should I start? It runs good everywhere else and I don’t want to totally destroy the tune while chasing this damn stumble. I unhooked the vacuum pod and plugged it and the stumble was totally gone, but I would like to keep the vacuum advance.
Is that 22* with or without the vacuum advance hose plugged?
I ask because at .045" t-slots that could be bringing on the vac advance a little. Probably not, but always good to be sure.
Timing is 22/34 Vacuum pod is plumbed to spark port.
Well here's the other possibility.
18 to 22 at 800 rpm is a reasonable range for initial with your cam IMO.
34 as the mechanical maximum should be OK.
However the curve could be too quick, or the vacuum advance could be contributing at too low of vacuum.
Measure the timing at 1200, 1800, 2400 rpm, (or more if you want).